Heating of coker cyclone and outlet



- April 26, 1960 ca. P. CANEVARI HEATING OF COKER CYCLONE AND OUTLETFiled April 2, 1957 FlG.-l

Ravi

Inventor Gerard P. Canevori By C Wflorney HEATING F COKER CYCLONE ANDOUTLET Gerard P. Canevari, Metuchen, N .J., assignor to Esso Researchand Engineering Company, a corporation of Delaware Application April 2,1957, Serial No; 650,253

1 Claim. (Cl. 208-48) from.

There has recently been developed an improved process known as the fluidcoking process for the production of fluid coke and the thermalconversion of heavy hydrocarbon oils to lighter fractions, e.g., see US.Patents 2,735,349 and 2,735,806.

The fluid coking process unit consists basically of a reaction vesseland a heater or burner vessel. In a typical operation the heavy oil tobe processed is injected into the reaction vessel containing a dense,turbulent, fluidized bed of hot inert solid particles. A staged reactorcan be employed. Uniform temperature exists in the coking bed.'. Uniformmixing in the bed results in virtually isothermal conditions and effectsinstantaneous distribution of the feed stock. In the reaction zone thefeed stock is partially vaporized and partially cracked. Effluent vaporsare removed from the coking vessel and sent to a fractionator for therecovery of gas and light distillates therefrom. Any heavy bottoms isusually returned to the coking vessel. The 'coke produced in the processremains in the bed coated on the solid particles. Stripping steam isinjected into the stripper to remove oil from the coke particles priorto the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generatedin the burner or heater vessel, usually separate. the reactor to theburner vessel, such as a fluid bed or transfer line burner, employing astandpipe and riser system; air being supplied to the riser forconveying the solids to the burner. Sufiicient coke or addedcarbonaceous matter is burned in the burner vessel to bring the solidstherein up to a temperature sufficient to maintain the system in heatbalance. The burner solids are maintained at a higher temperature thanthe solids in the reactor. Coke, equivalent to about based on feed, isburned for this purpose. This may amount to approximately 15% to 30% ofthe coke made in the process. The net coke production, which representsthe coke make less the coke burned, is withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process includeheavy crudes, atmospheric and vacuum bottoms from crude, pitch, asphalt,other heavy hydrocarbon petroleum residua or mixtures thereof. Typicallysuch feeds can have an initial boiling point of about 700 F. or higher,an A.P.I. gravity of about 0 to 20, and a Conradson carbon residuecontent of about 2 to 40 wt. percent. (As to Conradson carbon residuesee A.S.T.M. Test D-l89-41.)

It is preferred to operate with solids having a particle size rangingbetween 100 and 1000 microns in diameter with a preferred particle sizerange between 150 and 400 microns. Preferaby not more than 5% has a par-A stream of coke is thus transferred from a ice ticle size below aboutmicrons, since small particles tend to agglomerate or are swept out ofthe system with the gases. While coke is the preferred particulatesolid, other inert particulate solids such as spent catalyst, pumice,sand, kieselguhr, Carborundum, and alumina can be employed.

Serious problems have been encountered in the development of this typeof coking process. Typically the product vapors are removed overheadthrough a cyclone or usually cyclones and confined outlet linestherefrom, located in the upper portion of the reactor. Since thesevapors leaving the coking bed are at or near their dew or condensationpoint, they readily condense. This condensation and consequent cokedeposition is particularly serious on the surfaces having a temperatureof about 700 to 1000 F. The consequent deposits on the inner surfaces ofthe cyclone and outlet line therefrom sometimes causes the pressure dropto increase to such an extent as to require the unit to be shut downperiodically for cleaning.

One proposed solution has been to inject hot solids into the dispersephase to prevent this deposition and condensation by heating the vaporsand by scouring deposited coke from the cyclone inlet. This has in turnnecessitated a separate hot solids riser system. The latter has provedto be difficult to operate and has given rise to difficulties. Thesedifliculties have included bridging of the solids across the hot solidslines, with resulting stoppage of flow, and erosion of the hot solidslines when aeration rates were increased to help prevent bridging. Therequired solids rate to the disperse phase is small compared to the rateof solids circulated from the heating to the coking zone. Thus, the hotsolids lines to the disperse phase are much smaller than the linescarrying the major solids circulation, and are, consequently, muchharder to keep flowing freely.

This invention provides an improved method of overcoming the cokedeposition. The method comprises injecting a controlled small amount ofan oxygen-containing gas into the cyclone to combust a portion of theproduct hydrocarbon vapors. The temperature of the inner surfaces arethereby raised to the extent that coke deposition is prevented.Preferably an additional small amount of oxygen-containing gas is alsoinjected into the confined outlet line leading from the cyclone.

While gases of various oxygen concentration can be employed, air ispreferred for reasons of economy. Only a small controlled amount of thegases is employed since localized heating only is desired. Nosignificant amount of heat is introduced into the reactor overheadproduct stream or is there any significant dilution of the reactorproducts themselves. Consequently the amount of air employed is fromabout 0.5 to 2 s.c.f.m. (standard cubic ft./min.) per 1000 cu. ft.reactor effluent. This is total amount and would be divided into thenumber of injection points.

This invention will be better understood by reference to an example andthe flow diagram. The flow diagram is shown in Figure 1 and a moredetailed view of the cyclone and outlet line in Figure 2.

Referring now to the drawings, numeral 1 is a coking vessel constructedof suitable materials for operation at 950 F. A bed of coke particlespreheated to a suflicient temperature, e.g., 1125 F., to establish therequired bed temperature of 950 F. is made up of suitable parti cles ofto 400 microns. The bed of solid particles reaches an upper levelindicated by the numeral 5. Above is disperse phase 6. The bed isfluidized by means of a gas such as stripping steam entering the vesselat the stripping portion near the bottom thereof via pipe 3. Thefluidizing gas plus vapors from the coking reaction pass upwardlythrough the vessel at a velocity of 1 ft./sec. establishing the solidsat the indicated level. The fiuidizing gas serves also to strip thevapors and gases from the coke which flows down through the vessel tothe heater, not shown. A stream of solid particles is removed from thecoking vessel via line 8 and transferred to the heater.

A reduced crude oil to be converted is introduced into the bed of hotcoke particles via line 2, but preferably at a plurality of points inthe system. The oil upon contacting the hot particles undergoesdecomposition and the vapors resulting therefrom assist in thefiuidization of the solids in the bed and add to its general mobilityand turbulent state. The product vapors leave through cyclone separator7 and confined outlet 4-. As stated previously, several cyclones perstage can be employed with air injected into each one.

Typically the outlet lines are insulated or steam traced at 9 in aneffort to maintain a temperature suflicient to prevent coke deposition.Quite often this is ineffective. Coke deposition is known to beparticularly severe at points 10 and 11 because the inner surfacetemperature drops to 10-20 F. below reactor etfiuent temperaturedepending upon many factors such as insulation, steam tracing, etc. Toprevent this from happening air is injected at cyclone inlet 12 throughline 13 in an amount of /6 s.c.f.m. per 1000 cu. ft. of reactor efiluentat design conditions, and conveniently also into confined outlet line 4through lines 14 and 15 in an amount of /3 s.c.f.m. per 1000 cu. ft. ofreactor eflluent at design conditions. A small controlled amount ofproduct vapors are thereby combusted providing local heating whichraises the temperature at points 10 and 11 well above reactor effiuenttemperature. The combustion zone temperature is approximately 3000 F.although this is very localized and dissipated quickly by the efiiuentstream. Coke deposition is thereby completely prevented.

The advantages of this invention will be apparent to those skilled inthe art. Coking of the cyclone andoutlet line is prevented in a simple,economical manner with the consequent avoidance of plant shutdowns. Nosignificant amount of heat is introduced into the vapors to degrade themthermally and dilution problems are also avoided.

The conditions usually encountered in a fluid coker for fuels are alsolisted below for completeness.

Conditions in heater It is to be understood that this invention is notlimited to the specific examples which have been offered merely asillustrations and that modifications may be made without departing fromthe spirit of the invention.

What is claimed is:

In a process for coking a heavy hydrocarbon oil charge stock bycontacting the charge stock at a coking temperature with a dense,turbulent, fluidized bed of inert particulate solids in a coking zonewherein the oil is converted to product vapors and carbonaceous solidsare continuously deposited 011 the coke particles, removing efiluentproduct vapors through a cyclone separating zone and a confined outletline and wherein coke tends to deposit on the inner surfaces of thecyclone separating zone and said outlet line, the improved method ofpreventing coke deposition in said cyclone separating zone and saidoutlet line therefrom which consists in injecting a controlled smallamount of only air directly into the inlet of said cyclone separatingzone and directly into said confined outlet line therefrom to burn onlya small portion of the effiuent stream of product vapors at localizedconfined regions to quickly obtain localized heating and temperatureshigher than that of the effiuent stream of product vapors at the regionsof fair injection without introducing any insignificant amount of heatinto the effluent stream of product vapors and without any significantdilution of said efiiuent stream of product vapors whereby cokedeposition is prevented and the localized heating is quickly dissipatedby the effiuent stream of product vapors, the total amount of airinjected into said cyclone separating zone inlet and into said confinedoutlet line being in the range between about 0.5 and 2 s.c.f.m./1000cubic feet of efiluent stream of product vapors.

References Cited inthe file of this patent UNITED STATES PATENTS1,987,972 Rhein et al. Jan. 15, 1935 2,485,315 Rexet al. Oct. 18, 19492,549,117 Nelson Apr. 17, 1951 2,793,173 Fritz .May 21, 1957

